This article shows how to mark a message as Not Junk/Spam using an iPhone device. The steps below also work for other email providers such as Outlook and Yahoo.
1. Go to your Mailboxes and tap on Junk.
2. Depending on your Swipe Options, swipe left/right and tap on the three dots. On this screenshot, the message was swiped to the left.
3. Tap on Mark...
4. Select Mark as Not Junk.